This invention relates to liquid crystal controlled mirror systems. The usual liquid crystal controlled mirror comprises a liquid crystal unit disposed over a mirrored reflecting surface with the liquid crystal unit being selectively energized via an electric circuit. The preferred embodiment of the invention disclosed herein is a rearview mirror system of an automotive vehicle.
Liquid crystal controlled rearview mirror systems have heretofore been proposed for automotive applications. Some of applicant's own inventions disclosed in prior patents and pending applications, and commonly assigned, have involved liquid crystal controlled mirror systems. Illustrative of some uses of liquid crystal controlled mirrors are day/night rearview mirrors and mirrors for selectively expanding the field of view to the rear under certain operating conditions, such as when the vehicle turn signals are being operated.
The practice in the past has been to operate liquid crystal controlled mirrors by switching the liquid crystal medium between two extremes, one of maximum transparency (i.e. maximum reflectivity) and the other of maximum opaqueness (i.e. minimum reflectivity). In a day/night liquid crystal controlled rearview mirror of that type, a photocell sensed the presence of headlights from the rear and was operable to switch the mirror from its maximim reflectivity to its minimum reflectivity condition. When the headlamps were no longer incident on the photocell, the mirror reverted to its maximum reflectivity state. U.S. Pat. Nos. 3,862,798; 4,200,361; U.K. Patent Application No. 2,029,343; and German Offenlegungsschrift No. 2,808,260 illustrate such prior mirrors.
Another practice in the past has been to place the liquid crystal unit directly over the reflecting surface such that the two are in parallel planes. Because a liquid crystal unit comprises a number of optical interfaces there are inherent first surface reflections of the field of view at these interfaces, even though they are of substantially less intensity than the desired reflection from the mirrored surface. Since the image which is intended to be reflected to the observer is that which is reflected by a mirrored reflecting surface alone, first surface reflections from the additional optical interfaces can impair the quality of the image presented to the observer. The extent to which these can be troublesome can be severe enough to render this type of mirror commercially unacceptable for certain uses. German Offenlegungsschrift No. 2,808,260 has proposed to incline the plane of the liquid crystal unit relative to the plane of the mirrored reflecting surface.
The present invention relates to improvements in liquid crystal controlled mirror systems, and in the usage of the invention disclosed herein the improvements are illustrated in connection with a rearview mirror system of an automotive vehicle. The improvements contemplated by the present invention involve a number of different aspects.
For one, the construction of the liquid crystal controlled mirror assembly itself comprises a new and unique arrangement and organization of components which can provide a self-contained unit suited for both original equipment manufacture (OEM) and after-market. With this aspect of the improvement, controls for the mirror are entirely self-contained within the mirror assembly itself, and these provide for automatic and/or manual adjustment of the operating characteristics to suit particular operating conditions and/or a particular occupant of the vehicle who is using the mirror. Thus the invention is compact, readily installable, versatile, and adaptable to the user's needs.
Another aspect of the invention, in a particular embodiment thereof which uses light polarizers as part of the liquid crystal unit, involves the cooperative organization and arrangement of the liquid crystal unit and reflecting surface in relation to the geometry of the automotive vehicle within which the mirror is disposed. This offers a solution to the first surface reflection problem described above in liquid crystal controlled mirrors where the liquid crystal unit and the reflecting surface are in parallel planes. The improvement provided by this aspect comprises the liquid crystal unit being disposed in a plane which is at a small acute angle to the plane of the reflecting surface with the mirror assembly being disposed in the vehicle such that any inherent first surface reflections from the liquid crystal unit which would be presented to the observer are not from the desired rear field of view through the vehicle backlight, but rather are obtained from an inactive, non-distracting portion of the vehicle's interior, particularly the headliner. A particular advantage of this aspect of the invention is that observer attention can be better directed to the desired rear field of view presented by the mirrored reflecting surface and with virtual elimination of distractions to that field of view from inherent first surface reflections from the optical interfaces of the liquid crystal unit.
In another particular embodiment which does not use polarizers as part of the liquid crystal unit, the mirrored surface can be in a parallel plane to that of the liquid crystal unit. Indeed, a very compact construction is possible by making the mirrored surface a part of the liquid crystal unit itself.
Another of the aspects of the invention involves the achievement of a new mode of operation of a liquid crystal controlled mirror whereby the degree of opaqueness of the liquid crystal solution can be controlled over a range of different opaquenesses to achieve varying degrees of reflectivity in response to varying lighting conditions, such as incident light on the mirror. This capability is achieved in the preferred embodiment through the disposition of a light sensing device between the liquid crystal unit and the reflecting surface such that light from the rear field of view which is incident on the sensor is attenuated by the degree of opaqueness of the liquid crystal solution. The light sensor is operatively coupled in a closed loop control with the liquid crystal unit such that opaqueness of the liquid crystal medium is caused to faithfully respond to variations in the incident light intensity so as to maintain a level of incidence on the reflecting surface in accordance with a command input level which is set by the observer to his or her own preference. In this way the reflected field of view seen by the observer is automatically regulated in intensity by automatic compensation for variations in incident light from the field of view whose full effect would otherwise be seen by the observer. This aspect, both independently and in conjunction with other aspects, provides a new and unique mode of operation of a liquid crystal controlled mirror.
New embodiments of electronic controls for the liquid crystal controlled mirror are disclosed. In one of these embodiments the functional result is a mirror which will exhibit full brightness (i.e. maximum reflectivity) except that when headlamps or any other high intensity light coming from the rear strikes it, the liquid crystal solution is automatically adjusted in opaqueness to attenuate the high intensity incident light in accordance with a user preset level. Presetting of the user's preferred level may be accomplished by means of adjustment of a suitable device such as a potentiometer.
In another embodiment of electronic control a further light sensor is employed to sense the level of ambient light. The control operates to maintain the reflected light level equal to a multiple of the sensed ambient light level. This multiple can be preset by the user in accordance with his or her preference. An advantage of using the ambient light sensor is to adjust for the inherent sensitivity in the user's eyes which changes with the ambient light level.
The foregoing features, advantages, and benefits of the invention in various aspects, both individually and collectively, along with additional features, advantages, and benefits will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.